Well stimulation apparatus and a method of use thereof

ABSTRACT

The present disclosure relates to a well-stimulation apparatus with one or more elongated tie rods, at least one sealing assembly coupled to the one or more tie rods, and a stimulation material for generating a pressure event. The pressure event can stimulate a targeted portion of a geological formation that is positioned about an isolated portion of the wellbore. The pair of sealing assemblies are actuatable between a dormant condition for moving the well-stimulation apparatus in a wellbore and an active condition for defining the isolated portion of the wellbore.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to an apparatus, system and method for stimulating a targeted portion of a geological formation that is proximal to a well. In particular, the present disclosure relates to an apparatus, system and method that can create a sealed portion of a wellbore and that uses fluids to stimulate the targeted portion of the geological formation that is proximal the sealed portion of the well.

BACKGROUND

Well stimulation is a process that is used in oil and gas industry for collecting and extracting fluids, such as hydrocarbons, from a subterranean geological-formation. Well stimulation facilitates a production of fluids from the subterranean geological-formation and it may include the steps of perforating any wellbore tubulars, fracturing the geological formation, injecting fluids into the geological formation, and/or other stimulation operations.

Known hydraulic well-stimulation operations first isolate of a portion of the wellbore with one or more isolation mechanisms. The isolated portion of the wellbore is proximal to a region of the geological-formation that is targeted for stimulation. Next fluids are injected from the surface at high pressures for stimulating the targeted region of the formation through the isolated portion of the wellbore. After stimulation, the isolation mechanisms are deactivated, and a next wellbore portion may be isolated for stimulation. Hydraulic fracturing faces many challenges including but not limited to: long lead times to build enough pressure to cause stimulation, for example typical hydraulic fracturing operations require 10 to 100 minutes for building adequate pressure; large volumes of water are required, for example 5 million gallons of water per well can be a typical water usage; and large amounts of proppant are required, for example 300, 000 pounds to 4, 000, 000 pounds of sand can be required. Furthermore, the fractures generated during hydraulic well-stimulation operations can be limited to two radial opposed fractures within the isolated portion of the wellbore.

Propellant-based or gas-based well stimulation is also known. For example, a gas-based well stimulation creates a pressure event by generating a high-pressure gas that flows from the well to stimulate the targeted region of the formation. However, many known gas-based stimulation operations are restricted to vertical well sections, the pressure event is of a short duration and the pressure event is typically not focused within the desired target area of the geological formation. These characteristics of known gas-based stimulation operations can result in an ineffective stimulation.

SUMMARY

The embodiments of the present disclosure relate to an apparatus, system and method that create a pressure event within an isolated region of a well. The pressure event is of sufficient amplitude and duration that it can be used to stimulate a targeted region of a geological formation.

Some embodiments of the present disclosure relate to a well-stimulation apparatus that comprises: a tie rod with a first end and a second end; a stimulant-material container that is configured to be secured about the tie rod; and a sealing assembly that is couplable to the first end of the tie rod, the sealing assembly being actuatable between a dormant condition and an active condition for isolating a portion of a wellbore.

Without being bound by any particular theory, the embodiments of the present disclosure avoid the use of large volumes of water and proppant that are typically required of other known stimulation operations. Furthermore, the embodiments of the present disclosure create a pressure event by deflagrating a stimulant and focusing that pressure event from within the isolated portion of the wellbore into the target region of the geological formation so that new fractures can be created along with opening up of existing low-cohesion fractures and high-cohesion fractures. The embodiments of the present disclosure can be used to stimulate new wells, wells that require re-entry and even wells with damaged completions.

Furthermore, the embodiments of the present disclosure may provide further benefits such as, but not limited to: retaining and focusing a pressure-event from within an isolated portion of the wellbore into a target region of the geological formation; tailoring a profile of the pressure event to meet desired specifications or requirements; maintaining the position and integrity of apparatus within the isolated portion of the wellbore during the pressure event; sealing a portion of the well without exclusively relying on elastomeric materials; and positively locating the sealing elements in relation to one another without damaging or jamming other portions of the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a system for stimulating a target region of a geological formation that is proximal to a vertical well;

FIG. 2 is a schematic diagram showing an example of a system for stimulating a target region of a geological formation that is proximal to a horizontal section of a well;

FIG. 3 is a side-elevation view of an apparatus, according to some embodiments of the present disclosure, the apparatus for use with a system for stimulating a target region of a geological formation;

FIG. 4 is a cross-sectional view of the apparatus shown in FIG. 3 taken along the section line A-A shown in FIG. 3;

FIG. 5 is a side-elevation view of the apparatus shown in FIG. 3, with a gas-generator assembly removed for showing further components of the apparatus;

FIG. 6 shows one embodiment of a tie rod for use with the apparatus shown in FIG. 4, wherein FIG. 6A shows a side-elevation view of the tie rod; FIG. 6B shows an enlarged portion of the tie rod, as identified by a circle A in FIG. 6A; and FIG. 6C shows an enlarged, side-elevation view a portion of the tie rod, as identified by a circle B in FIG. 6A;

FIG. 7 is enlarged, cross-sectional view of two portions of the apparatus shown in FIG. 4, wherein FIG. 7A shows an enlarged, side-elevation view of a portion of the apparatus, as identified by a circle Y in FIG. 4; and FIG. 7B shows an enlarged, side-elevation view of a portion of the apparatus, as identified by a circle X in FIG. 4;

FIG. 8 is a side-elevation view of a sealing assembly in a non-sealing position for use with the apparatus shown in FIG. 3;

FIG. 9 is a cross-sectional view of the sealing assembly shown in FIG. 8 along the section line B-B shown in FIG. 8;

FIG. 10 is a side-elevation view of the sealing assembly shown in FIG. 8 shown in a sealing position;

FIG. 11 is a cross-sectional view of the sealing assembly taken along section line E-E shown in FIG. 10;

FIG. 12 is an enlarged cross-sectional view of a portion of the sealing assembly, as identified by circle Z shown in FIG. 9 with sealing elements positioned at an angle of repose;

FIG. 13 is an enlarged cross-sectional view of a portion T of the sealing assembly, as identified by circle T in FIG. 11, showing the sealing elements positioned in a sealing position with an angle of attack;

FIG. 14 shows one embodiment of an actuation gas-generator body according to the present disclosure, the actuation gas-generator body for use with the apparatus shown in FIG. 4, wherein FIG. 14A shows a rear-isometric view of the actuation gas-generator body; FIG. 14B shows a front, isometric view of the actuation gas-generator body; FIG. 14C shows rear, elevation view of the actuation gas-generator body; FIG. 14D shows a side elevation view of the actuation gas-generator body; and FIG. 14E shows an enlarged portion of the actuation gas-generator body, as identified by circle A in FIG. 14C;

FIG. 15 shows one embodiment of a piston housing according to the present disclosure, the piston housing for use with the apparatus shown in FIG. 4, wherein FIG. 15A shows a side-elevation view of the piston housing; and FIG. 15B shows a cross-sectional view of the piston housing taken along section line D-D shown in FIG. 15A;

FIG. 16 is a perspective view of a sealing element of the sealing assembly shown in FIG. 8;

FIG. 17 is a top-plan view of the sealing element shown in FIG. 16;

FIG. 18 is a bottom-plan view of the sealing element shown in FIG. 16;

FIG. 19 is a cross-sectional view of the sealing element taken 11 along the section line C-C shown in FIG. 16;

FIG. 20 is a schematic diagram showing a coupling of at least two of the apparatus shown in FIG. 3;

FIG. 21 is a schematic diagram showing a controller having more than one switch in a parallel connection for controlling at least one of the apparatus shown in FIG. 20;

FIG. 22 is a series of schematic diagrams that show a controller with more than one switch in a serial connection and progressing through a sequence for controlling at least one of the apparatus shown in FIG. 3, wherein FIG. 22A shows the controller in an inactivated arrangement and FIG. 22B, FIG. 22C and FIG. 22D show further steps of an activation sequence;

FIG. 23 is a schematic diagram showing a controller according to further embodiments of the present disclosure this controller has a processor for controlling the multiple apparatus shown in FIG. 20;

FIG. 24 is a schematic side view of a knuckle connector for use with the systems of the present disclosure;

FIG. 25 is a series of schematic diagrams that show the knuckle connector shown FIG. 24 connected at one end to the apparatus shown in FIG. 3 and to a line from the surface at the other end, wherein FIG. 25A shows the knuckle connector in a substantially central position;

FIG. 25B shows the knuckle connector in a first position to accommodate movement of the line from surface and FIG. 25C shows the knuckle connector in a second position to accommodate movement of the line from surface;

FIG. 26 shows another embodiment of an apparatus, according to the present disclosure, the apparatus for use with a system for stimulating a target region of a geological formation, wherein FIG. 26A is a side-elevation view of the apparatus; and FIG. 26B is a cross-sectional view taken along section line A-A shown in FIG. 26A; and

FIG. 27 shows another embodiment of a sealing element, wherein FIG. 27A shows a top-plan view of the sealing element; FIG. 27B shows a perspective view of the sealing element; FIG. 27C shows a side, perspective view of the sealing element, FIG. 27D shows a cross-sectional view of the sealing element taken through section line A-A shown in FIG. 27C; and FIG. 27E is a cross-sectional view taken through section line A-A as shown in FIG. 27C but of a different embodiment of the sealing element.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to an apparatus and a system that includes the apparatus. The apparatus and system can be used for isolating a portion of a well, which may also be referred to as a wellbore, and for stimulating a target region of a geological formation that is proximal to the isolated portion with a pressure event. The apparatus and system are configured to generate the pressure event by deflagrating stimulant materials and focusing the energy of the pressure event into the target region. The pressure event may be tailored to meet predetermined requirements to affect a desired stimulation of the target region of the geological formation.

In some embodiments of the present disclosure, the apparatus comprises one or more tie rods that are fixed at each end to one or more sealing-elements. The one or more tie rods maintain a substantially constant distance between the opposing sealing-elements during the pressure event.

In some embodiments of the present disclosure, the apparatus comprises a plurality of stacked, actuatable sealing elements. The sealing elements may be dry or, optionally, coated with a viscous and/or deformable sealing material such as a grease. The sealing elements may be actuated between a sealing position and a non-sealing position. The sealing position may also be referred to herein as the active condition and this position is useful for forming an imperfect fluid-tight seal against an inner surface of the well. The person skilled in the art will appreciate that when this seal is formed, while the sealing elements are in active condition, some fluids and/or energy from the pressure event may escape therepast. Permitting some fluids and/or energy to escape past the sealing elements provides a relief that may avoid causing damage to the apparatus or the wellbore the apparatus is positioned within. However, when the sealing elements are in the active condition they focus the fluids and/or energy from the pressure event into the target region for stimulation thereof. As described further below, the active condition may be a temporary condition. The non-sealing position may also be referred to herein as a dormant condition and this position may be useful for when the apparatus and/or the system are moved within the wellbore.

In some embodiments of the present disclosure, the sealing elements may be actuated to the active condition by an actuation body such as, but not limited to: an actuation gas-generator, a hydraulic-pressure driven mechanism, a pneumatic-pressure driven mechanism, a mechanical mechanism such as a spring, an electric motor, an electric solenoid, or combinations thereof. The sealing elements may be maintained in the active condition by a high-pressure gas that is generated during the pressure event by deflagrating a stimulant material that is housed by the apparatus. The sealing elements may return to the non-sealing position by a passive mechanism or: a further gas-generator, a hydraulic-pressure driven mechanism, a pneumatic-pressure driven mechanism, a mechanical mechanism such as a spring, an electric motor, an electric solenoid, or a combination thereof.

FIG. 1 and FIG. 2 show a typical wellsite 100 where a well-stimulation process is being conducted.

The wellsite 100 comprises a wellbore 102 formed under a rig 104 and extending down from the surface into a subterranean formation 106. The wellbore 102 may be a vertical wellbore as shown in FIG. 1, or a horizontal well (as shown in FIG. 2) that extends substantially vertically from the surface down to a predetermined depth and then deviates to a substantially horizontal section. As is known in the art, the wellbore 102 may be cased using a perforated casing tubular or the wellbore 102 may be uncased.

A line from surface 108 extends from the surface into the wellbore 102 and is connectible at one end to one or more well-stimulation apparatuses 120. In some embodiments of the present disclosure, the line 108 is a conduit for conducting fluids between the surface and proximal the one or more well-stimulation apparatus 120. Some examples of the types of conduit include, but are not limited to: jointed pipe and coiled tubing. In some embodiments of the present disclosure, the line 108 comprises one or more conductors for transmitting electrical information between the surface and the one or more well-stimulation apparatuses 102. Some examples of the types of wires include wireline, slick line and electrical line. In some embodiments of the present disclosure, the line 108 comprises both a conduit and a wire. The line 108 is connectible to one or more well-stimulation apparatuses 120 that are each located at a desired location in relation to the subterranean formation 106. Each well-stimulation apparatus 120 comprises two sets of sealing elements 122 about the two opposite ends thereof for isolating a portion of the wellbore 102. The apparatus 120 further comprises a gas-generator assembly 126 that can create a pressure event by generating a flow of high-pressure fluid 124. The high pressure-fluid flows from the sealed portion of the wellbore 102 radially outwardly to stimulate a targeted region of the subterranean formation 106 that is in proximity to the sealed portion.

FIG. 3 is a side view of a well-stimulation apparatus 120, according to some embodiments of the present disclosure. The well-stimulation apparatus 120 comprises a gas-generator assembly 126 and at least one sealing assembly 128, but preferably a pair of opposed sealing assemblies 128 that are arranged along a longitudinal axis (defined by line A-A in FIG. 3) of the well-stimulation apparatus 120. The opposed sealing assemblies 128 are spaced apart from each other with the gas-generator assembly 126 positioned therebetween. In the example shown in FIG. 3, each of the two sealing assemblies 128 are positioned proximal to one of the opposite ends 130A, 130B of the well-stimulation apparatus 120.

Referring to FIG. 4, the gas-generator assembly 126 comprises an elongate tie rod 132 that is configured to receive a stimulant-material container 134 thereabout. In some embodiments of the present disclosure, the stimulant-material container 134 is in a form of one or more sleeves that are configured to be secured about the tie rod 132 and to receive stimulant material therein. The tie rod 132 is made of a rigid material with a high tensile-strength, such as steel. The tie rod 132 is configured with a strength that can bear a tensile load that is generated by the pressure event created during operation of the apparatus 120. The person skilled in the art will appreciate that various materials are suitable for bearing this tensile load, including various types of steel and iron. In some embodiments of the present disclosure, the tie rod 132 is made of maraging steel and has a cross-sectional area about 1/3.84 of the cross-sectional area of the well bore 102. The tie rod 132 can bear the tensile load generated by a pressure event with a peak pressure of between about 10, 000 pounds per square inch (psi) and 50, 000 psi.

As shown in FIG. 4, FIG. 7 and FIG. 5, the tie rod 132 can be coupled to the two sealing assemblies 128 at the two ends thereof using a fastener 136. As the person skilled in the art will appreciate, the fastener 136 can be any type of mechanical fastener that will be able to keep the tie rod coupled 132 to a sealing assembly 128 at each end in the face of the tensile load generated by the pressure event. The person skilled in the art will also appreciate that the fastener 136 includes other types of connections that are made by fastening methods including welding, interference fit, brazing, riveting and combinations thereof. Types of suitable mechanical fasteners 136 include, but are not limited to: a machine screw, a bolted flange, a clamped flange and a buttress-threaded or other type of threaded connection. FIG. 6A shows one example of a buttress-threaded connection at each of a first end 132A and a second end 132B. FIG. 6B shows the first end 132A with a first threaded-member 133A that can extend at least partially about the first end 132A in an outward helical fashion. FIG. 6C shows the second end 132B with a second threaded-member 133B that can extend at least partially about the second end 132B in an outward helical fashion. The first threaded-member 133A and the second threaded-member 133B can define an angle (as compared to the longitudinal axis of the apparatus 120) that is the same or different. As will be appreciated by those skilled in the art, if the fastener 136 is a buttress-threaded connection, then the first threaded-member 133A can be oppositely configured than the second threaded-member 133B to allow the tie rod 132 to better maintain the connection formed with the sealing elements 128 when stressed by the tensile load that is generated during the pressure event.

In some embodiments of the present disclosure, an optional machine screw 138 may be used to further fasten each sealing assembly 128 to the tie rod 132. The machine screw 138 can help maintain the coupling between the tie rod 132 and the sealing assemblies 128 during operation of the well-stimulation apparatus 120 and in the event the fastener 136 fails.

In some embodiments of the present disclosure, the tie rod 132 may have a length suitable for isolating a wellbore portion as needed. In some other embodiments, the length of the tie rod 132 may be designed depending on how much stimulant material will be used and/or other well characteristics. In other embodiments of the present disclosure, the apparatus 120 may be provided with more than one tie rod 132 of the same or different lengths. An operator may select a tie rod 132 with a desired length when assembling the well-stimulation apparatus 120 on a wellsite 100.

The tie rod 132 establishes the positions of the sealing assemblies 128 relative to each other and, therefore, the tie rod 132 is considered to facilitate positive locating of the sealing elements 122 to define the isolated portion of the wellbore 102. The tie rod 132 prevents the sealing assemblies 128 from moving under the forces generated during the pressure event. The tie rod 132 may further serve as a support structure for the stimulant-material container 134.

As shown in FIG. 4 and FIG. 7, the stimulant-material container 134 can comprise an inner wall 142, an outer wall 144, and a stimulant material 146 that is positioned within an annulus that is defined by the inner and outer walls 142 and 144. The stimulant material 146 (also referred to as “stimulation propellant”, “propellant”, “stimulant material”, “stimulant materials” or “stimulant” herein) is a material that may be ignited, deflagrated, combusted, exploded or combinations thereof to generate the pressure event that is defined by a flow of high-pressure gas from the apparatus 120 for the purpose of stimulating the targeted region of the surrounding geological formation.

In some embodiments of the present disclosure the stimulant material 146 comprises a matrix in which a fuel or a mix of a fuel and an oxidizer can be embedded. The stimulant material 146 is preferably stable at or below the temperature (less than about 100° C.) and pressure (less than about 2000 psi) that are typically found within the wellbore 102.

In some embodiments of the present disclosure, the matrix is a polymer-based binder that is selected from, but not limited to: polysulfides; polybutadieneacrylic acids; polybutadiene-acrylonitriles; polyurethanes; carboxyl-terminated polybutadienes; hydroxyl-terminated polybutadienes; polyvinyl chlorides; acrylonitrile-butadiene-styrenes or combinations thereof. In some embodiments of the present disclosure, the preferred matrix comprises hydroxyl-terminated polybutadienes.

In some embodiments of the present disclosure the fuel may be: a metal, a non-metal or combinations thereof. For example, the metal may be one or more of, but is not limited to: aluminum, magnesium, zinc, iron or copper. The non-metal may be, but is not limited to: boron, silicon or combinations thereof. The fuel may be in a powdered form or not. The fuel may be a compound, an alloy or combinations thereof.

In some embodiments of the present disclosure the oxidizer may be: an oxygen donating salt; an inorganic perchlorate compound, such as ammonium perchlorate or potassium perchlorate; an inorganic nitrate, such as ammonium nitrate or potassium nitrate, a nitraminde, such as cyclotrimethylene trinitramine, or cyclotetramethylene, or combinations thereof. In some embodiments of the present disclosure, the preferred oxidizer is ammonium perchlorate.

In some embodiments of the present disclosure the matrix and the fuel may be the same component of the stimulant material 146. For example, this component may be polyester based, such as polystyrene or polypropylene; cellulose based such as nitrocellulose; or some other form of energetic polymer. In these embodiments, the stimulant material 146 comprises an oxidizer and a combined, single fuel/matrix component.

Optionally, the stimulant material 146 may also comprise other components such as, but not limited to: a hardening agent; a curing agent; a burn-rate catalyst; a burn-rate inhibitor or combinations thereof.

As one skilled in the art will appreciate, there are various forms of the stimulant material 146 that are suitable but not specifically named herein.

In some embodiments of the present disclosure deflagrating the stimulant material can generate the pressure event with a peak pressure of between about 10, 000 psi and 50, 000 psi. In some embodiments of the present disclosure the pressure event can have a peak pressure between about 15, 000 psi and 40, 000 psi. In further embodiments of the present disclosure the pressure event can have a peak pressure between about 20, 000 psi and about 30, 000 psi. In some embodiments of the present disclosure the time to build to the peak pressure (which is also referred to as “pressure rise time” herein) is between about 10 milliseconds to about 1000 milliseconds. In some embodiments of the present disclosure, the total duration of the pressure event is between about 10 milliseconds and 20 seconds.

As shown in FIG. 7A, one or more stimulation-activation devices 148, also denoted as initiators, are embedded in or otherwise coupled to the stimulant-material 146 for igniting the stimulant-material 146. Igniting the stimulant-material 146 initiates deflagration of the stimulant-material 146. In some embodiments of the present disclosure, the stimulation-activation device 148 is an electrical ignition device and comprises an electrical input terminal 150 electrically connected to a controller (as described herein below).

In some embodiments of the present disclosure, the outer wall 144 of the stimulant-material container 134 is a wall that is at least partially consumable. For example, the outer wall 144 may comprise a thin layer of plastic, metal, or the like, that may be broken, disintegrated, consumed or otherwise at least partially consumed by the flow of high-pressure gas when the stimulant material 146 is ignited and deflagrates. Partial or complete consumption of the outer wall 144 allows the generated high-pressure gas to flow out of the stimulation gas-generator assembly 126 with minimal impediment. In other embodiments of the present disclosure, the outer wall 144 may be made of a rigid material such as steel, and comprise a plurality of holes for the generated high-pressure gas to flow therethrough.

FIG. 8, FIG. 9 and FIG. 12 show the structures of a sealing assembly 128 configured in the dormant condition. As shown, the sealing assembly 128 comprises a mandrel 152 having the fastener 136 at a first end 156 thereof for coupling the sealing assembly 128 to the tie rod 132. The mandrel 152 may be coupled to an actuation body 154 at a second end 158 thereof using suitable couplers such as threaded fasteners, a bolt and nut and the like (not shown). The actuation body 154 also comprises a suitable coupler (not shown) for coupling to the line 108 or another sub such as another well-stimulation apparatus 120.

The mandrel 152 may define an aperture 164 adjacent the fastener 136 for receiving a bolt member 138 (see FIG. 7B) for further coupling the mandrel 152 to the tie rod 132. A longitudinal bore 162 extends from the second end 158 of the mandrel 152 to the bolt hole 164 for inserting the backup bolt 138 therethrough.

On the outer surface the mandrel 152 comprises a stop shoulder 170 that extends radially outwardly from the second end 158 thereof for supporting one end of a spring 192 (described further below). The outer surface of the mandrel 152 also defines a circumferential recess 172 near the second end 158, and with circumferential radial edges 174 that may be angled towards the first end 156. At least two sealing elements 122 are stacked within the circumferential recess 172 offset from each other. The sealing elements 122 are configured to be actuated between the dormant condition and the active condition for establishing the isolated portion of the wellbore 102. To actuate the sealing elements 122 between the dormant condition and the active condition an outer edge 182 (shown in FIG. 16) of each sealing element 122 are configured to move radially relative to a longitudinal axis of the apparatus 120 (shown as line A-A in FIG. 3) for engaging an inner wall of the wellbore 102 or a tubular therein. In some embodiments of the present disclosure an opposite inner edge 186 (see FIG. 16) of each sealing element 122 can be fixed to the recess 172, or not. When the inner edge 186 is not fixed, the inner edge 186 of each sealing element 122 may move within the recess 172 substantially parallel to the longitudinal axis of the apparatus 120.

Optionally, the outer surface of the mandrel 152 may also include two or more centralizing members 153 that are each configured to extend outwardly from the outer surface of the mandrel 152 and engage an inner surface of the wellbore 102 or an inner surface of casing that may be positioned between the mandrel 152 and the inner surface of the wellbore 102. While the drawings only show one centralizing member 153, the person skilled in the art will appreciate that at least two centralizing members 153, or preferably three or more, are required to centralize the mandrel 152 and, therefore, the well-stimulation apparatus 120 within the wellbore 102. The person skilled in the art will appreciate that various types mechanisms can be used to cause the centralizing members 153 to extend outward, including but not limited to: a hydraulic-pressure based mechanism, a pneumatic-pressure based mechanism, a mechanical mechanism such as a spring, electric motor, electric solenoid, or a combination thereof.

The sealing elements 122 are made of a material or materials that are suitable for bearing the pressure generated during the pressure event. In some embodiments of the present disclosure the sealing elements 122 may be dry or coated with a viscous sealing material such as grease, when being installed on the mandrel 152. In some embodiments of the present disclosure, the sealing elements 122 are made of 4140 steel. However, those skilled in the art will appreciate that the sealing elements 122 may be made of any suitable material such as, but not limited to: a metal, a metal alloy, a ceramic, an elastomer, or combinations thereof.

FIG. 8 shows various embodiments of the present disclosure where individual sealing elements 122 are denoted by a letter: 122A which is furthest from the first end 156, 122B, 122C, 122D, 122E and 122F, which is closest to the first end 156. The person skilled in the art will appreciate that this nomenclature is provided as an example only and it is not intended to limit the total number of sealing elements 122 of a sealing assembly 128.

In some embodiments of the present disclosure, all of the sealing element 122A through to the sealing element 122F are made of a rigid material. In some embodiments of the present disclosure, all of the sealing element 122A through to sealing element 122F are made of the same material that is a flexible material, an elastic material or combinations thereof. In some embodiments of the present disclosure, the sealing element 122A through to the sealing element 122F are made of the same material, or not. In some embodiments of the present disclosure, the sealing elements 122A and 122F are made of the same first material and the sealing elements 122B through to sealing element 122E are made of one or more materials. In these embodiments, the first material is more rigid than the one or more materials. In some embodiments of the present disclosure, the sealing element 122B is made of a material that is less rigid than the material or materials of the other sealing elements 122A and 122C through 122F are made of.

As shown in the embodiments of FIG. 16 through to FIG. 19, each sealing element 122 has an annulus sector or annular segment shape having a rounded outer edge 182, an arc-shaped circumferential groove 184 and a rounded inner edge 186. The groove 184 is used for fitting therein the spring 192 for providing a restoring biasing-force that holds the sealing element 122 in the dormant condition. The person skilled in the art will appreciate that groove 184 may be different shapes to fit the shape or orientation of the spring 192. The person skilled in the art will also appreciate that some embodiments of the present disclosure relate to sealing elements 122 that do not have the groove 184. In these embodiments, where the groove 184 is absent, the spring 192 may be multiple springs positioned between one or more adjacent sealing elements 122 for providing the restoring biasing-force to bias those sealing elements 122 into the dormant condition. The rounded inner edge 186 may provide a floating interface for engaging the recess 172. FIG. 27 shows further embodiments of the sealing elements 122 that have a flat outer edge 182A and a rounded inner edge 186A (FIG. 27D) or a flat inner edge 186B (FIG. 27E).

Referring to FIG. 9, the sealing elements 122 are arranged in the recess 172 of the mandrel 152 at an acute angle with respect to a reference longitudinal direction 176 (show in FIG. 12 and FIG. 13) and facing the first end 156 thereof. Herein, the angle between each sealing element 122 and the reference longitudinal direction 176 is denoted as an angle of repose α when the sealing elements 122 are configured in the dormant condition (see FIG. 12), and is denoted as an angle of attack β when the sealing elements 122 are configured in the active condition (see FIG. 13). Both the angle of repose α and the angle of attack β may be acute angles facing the first end 156 (therefore facing the center of the well-stimulation apparatus 120), and the angle of attack β is generally larger than the angle of repose α. In some embodiments, the angle of repose α is selected between about 0° and about 75°, the angle of attack β is selected between about 10° and about 80°.

Referring again to the non-limiting embodiment shown in FIG. 9, the sealing assembly 128 comprises a biasing assembly 190 on the outer surface of the mandrel 152 between the stop shoulder 170 and the sealing elements 122 for moving and/or releasably holding the sealing elements 122 in the dormant condition. In these embodiments, the biasing assembly 190 comprises the spring 192 arranged against the stop shoulder 170 for providing a biasing force towards the center of the well-stimulation apparatus 120 and a biasing collar 194 for engaging and for transmitting the biasing force to the sealing elements 122 thereto. As will be appreciated by those skilled in the art, other mechanisms can be used in place of the biasing assembly 190 for moving and/or holding the sealing elements 122 in the dormant condition.

The sealing assembly 128 also comprises an actuation assembly 200 for overcoming the biasing force of the biasing assembly 190 and actuating the sealing elements 122 to the active condition. As shown in FIG. 9, the actuation assembly 200 comprises an actuation sub 151 for actuating the sealing elements 122 to the active condition. In some embodiments of the present disclosure, the actuation sub 151 is configured to house an actuation body 154, a piston housing 202 having one or more pistons 204 movable therein and an actuation collar 206 for engaging the sealing elements 122 on the side thereof opposite to the biasing assembly 190. In some embodiments of the present disclosure, the actuation body 154 is an actuation gas-generator that comprises an actuation-propellant chamber 208 for housing an actuation propellant (not shown) for generating an actuation gas flow. FIG. 14 shows the actuation body 154 in greater detail. In particular, the actuation body 154 has two opposing ends 154A and 154B (see FIG. 14A and FIG. 14B). The end 154A defines a plurality of apertures 155 for receiving fastener members (not shown) that are used for fastening a cap 154C onto the end 154A the actuation body 154 within the sealing assembly 128. The first end 154A also defines one or more channels 157 (FIGS. 14C, 14D and 14E) that are configured to receive one or more wires or conduit lines (not shown) and for conducting the wires or conduit lines into the actuation propellant chamber 208 so that a signal (e.g. an electrical signal, pneumatic signal or hydraulic signal) can be communicated into the actuation propellant chamber 208 for directly igniting (or indirectly igniting through an actuation-activation device 214) the actuation propellant therein. Proximal the end 154B, the actuation body 154 comprises a mating section 159 for mating the actuation body 154 with the gas generator sub 151. For example the mating section 159 may be configured to be mateably received within the gas generator sub 151, for example by one or more mating members that are present on the outer surface of the mating section 159 and an internal surface of the gas generator sub 151. For example, the mating section 159 may comprise a threaded connection member that can be threadably connected with a corresponding threaded connection member on the gas generator sub 151. As one skilled in the art will appreciate, there are various different types of mating members that can be utilized to mate the actuation body 154 within the actuation sub 151.

The actuation-propellant chamber 208 is configured to be in fluid communication with one or more gas channels 212 and therethrough with an interior plenum of the piston housing 202. So that when ignited, the actuation propellant will deflagrate and generate a pressurized gas that can flow through the one or more gas channels 212, through the interior plenum and act against a face of the piston 204. Optionally, the actuation-propellant chamber 208 comprises a burst disc 210 that retains the actuation propellant within the actuation-propellant chamber 208 until such time that a pressure within the actuation-propellant chamber 208 exceeds the pressure rating of the burst disc 210. In some embodiments of the present disclosure the one or more pistons 204 can be a single annular piston that extends within a similarly annular piston housing 202 about an outer surface of the sealing assembly 128. In these embodiments, the interior plenum also extends annularly about the outer surface of the sealing assembly 128.

FIG. 15 shows an alternative embodiment of the piston housing 202. The piston housing 202 comprises one or more piston chambers 222 each movably receiving a piston 204 (not shown) therein. The piston housing 202 also comprises one or more gas passages 226 that act as the interior plenum to provide fluid communication between the one or more gas channels 212 and the one or more piston chambers 222. The piston housing 202 may be fixed to the mandrel 152 with the one or more gas channels 226 in fluid communication with the one or more gas channels 212.

Referring again to FIG. 8 and FIG. 9, after assembly, when the sealing assembly 128 is in the dormant condition the sealing elements 122 are biased by the biasing assembly 190 to occupy a radial position with the angle of repose α (as shown in FIG. 12). To actuate the sealing assembly 128 into the active condition, the actuation propellant in the actuation-propellant chamber 208 is ignited by an actuation-activation device 214, which may be an electrical ignition device. Ignition of the actuation-propellant causes the deflagration and generation of the pressurized gas. The pressurized gas flows through the one or more gas channels 212 into the passages in the piston housing 202. As shown in FIG. 10 and FIG. 11, the pressurized gas flow then actuates the one or more pistons 204 to move out of the piston housing 202, thereby driving the actuation collar 206 to overcome the biasing force of the biasing assembly 190 and actuate the sealing elements 122 generally upwardly to the angle of attack β. The sealing assembly 128 is then considered to be in the active condition.

Referring now back to FIGS. 1 and 2, one or more well-stimulation apparatuses 120 are connectible to the line 108 and extended into the wellbore 102 to a desired location. To isolate and stimulate a portion of the wellbore 102, the actuation body 154 generates the actuation pressure event whereby a flow of pressurized gas actuates the sealing assemblies 122 to the active condition, in which the sealing elements 122 are conditioned to the angle of attack for engaging an inner surface of the casing or of the wellbore to form a temporary seal within the wellbore 102. The temporary seal on both sides of the actuation body 154 defines the isolated portion of the wellbore 102. To stimulate the isolated portion of the wellbore, the stimulant material within stimulant-material container 134 of the stimulation gas-generator assembly 126 is ignited by the stimulation-activation devices 148 to deflagrate and generate high-pressure gas, which breaks or otherwise removes the consumable outer wall 144 and jets into the isolated wellbore portion, which is referred to herein as the pressure event. The actuated sealing elements 122 focus the generated high-pressure fluid and/or energy of the pressure event into the targeted portion of the geological formation 106. The term “focus” is used herein to refer to the sealing elements 122 directing substantially most or substantially all of the fluid and/or energy of the pressure event into the targeted portion with or without making one or more fluid-tight seals against an inner surface of the wellbore 102.

As described above, the sealing elements 122 are conditioned at the acute angle of attack β facing the center of the well-stimulation apparatus 120 to engage the casing or the wall of the wellbore 102. Such a configuration provides an advantage that the casing or the wall of the wellbore 102 supports the sealing elements 122 against the high pressure applied thereto.

In some embodiments of the present disclosure, the actuation of the sealing elements 122 by the actuation pressure event and the pressure event created by the gas-generator assembly 126 occur at about the same time or the actuation pressure event may occur earlier. The actuation gas is released after the sealing elements 122 are configured to the angle of attack β (i.e., to the active condition). The pressure event generated by the stimulation gas-generator assembly 126 may facilitate and maintain the sealing elements 122 in at the angle of attack β during the stimulation process of the isolation wellbore portion.

After stimulation, the pressure in the isolated wellbore portion is reduced with the high-pressure gas being released into the formation 106. The biasing assembly 190 then forces the sealing elements 122 to move back to the angle of repose α, thereby configuring the well-stimulation apparatus 120 to the dormant condition.

As described above, one or more well-stimulation apparatuses 120 may be used for well stimulation. A controller is used for controlling the ignition of the stimulant material and the actuation propellant in each well-stimulation apparatus 120. In some embodiments, fluid pressure may be used for triggering the controller to sequentially activate each well-stimulation apparatus 120 in a desired timing pattern. The switching pressures (described in more detail herein below) are provided by pumping down fluid from the surface through the line 108. In these embodiments, the switching pressures may be any suitable pressures such as between the ambient pressure and about 10, 000 psi. In some alternative embodiments, the switching pressures are between ambient and about 20, 000 psi. In some other embodiments, the switching pressures are between ambient and about 25, 000 psi. In some other embodiments, the switching pressures are between ambient and about 50, 000 psi.

FIG. 20 shows one embodiment of the present disclosure in which the line 108 has three well-stimulation apparatuses 120A, 120B and 120C and the downhole end thereof is positioned at a desired location of a wellbore 102 for well stimulation. As shown, the stimulation- and actuation-activation devices 148 and 214 (marked as “P” and “S” in FIG. 20) in each well-stimulation apparatus 120A, 120B, 120C are electrically connected in series to form an ignition circuit 232A, 232B, 232C (collectively denoted as 232). The three ignition circuits 232 are electrically connected to a pressure-actuated controller 234 in parallel via electrical wiring. In this example, the controller 234 is located downhole in the line 108.

As shown in FIG. 21, the controller 234 comprises a power source 236 such as a battery and three pressure-actuated normally-open Single-Pole-Single-Throw (SP ST) switches 238A, 238B and 238C that are connected to the power source 236 in parallel. Each switch 238A, 238B, 238C may be closed by a predefined threshold switching pressure (denoted as P1, P2 and P3 for switches 238A, 238B and 238C) that is applied thereto from the line 108 to activate one or more of the well-stimulation apparatus 120A, 120B or 120C. As the wiring in a well-stimulation apparatus 120 may be destroyed during well stimulation, it is preferably to activate the well-stimulation apparatuses 120 in a direction from downhole to uphole, i.e., from 120A to 120C, and therefore, P3>P2>P1. For example, P1=3000 psi, P2=5000 psi, and P3=7000 psi.

In operation, a fluid is directed through the line 108 to the controller 234. The fluid applies a pressure P to the controller 234 with P2>P>P1 to close switch 238A. The actuation-activation devices 214 and the simulation-activation device 148 of the well-stimulation apparatus 120A is activated. As a result, the sealing elements 122 of the well-stimulation apparatus 120A are actuated to form the isolated portion of the wellbore 102. At substantially the same time, or later, the stimulation gas-generator assembly 126 generates the pressure event defined by the flow of high-pressure gas into the formation 106 within the isolated portion of the wellbore 102.

Then, the fluid pressure P is increased to P3>P>P2 to close switch 238B. As a result, the sealing elements 122 of the well-stimulation apparatus 120B are actuated and seal the wellbore portion, and the stimulation gas-generator assembly 126 thereof generates high-pressure gas to stimulate the formation 106 about the sealed wellbore portion.

Then, the fluid pressure P is further increased to P>P3 to close switch 238C. As a result, the sealing elements 122 of the well-stimulation apparatus 120C are actuated and seal the wellbore portion, and the stimulation gas-generator assembly 126 thereof generates high-pressure gas to stimulate the formation 106 about the sealed wellbore portion.

In some embodiments of the present disclosure the wiring and the ignition circuit are usually destroyed after the activation of a well-stimulation apparatus 120, but there is a risk that short-circuit may still occur, thereby causing damage to the controller 234 and/or other well-stimulation apparatus 120. In some alternative embodiments, such a risk may be prevented by including time delay fuses in the controller 234, which will open the circuit after a pre-determined period of time.

FIG. 22A shows one example of the controller 234 as comprising a power source 236 and n pressure-actuated switches for controlling n well-stimulation apparatuses 120 (n being an integer greater than 1). The ignition circuits 232 of the n well-stimulation apparatuses 120 are denoted herein as the 1st, 2nd, n-th ignition circuits, and the n switches are denoted herein as the 0-th, 1st, 2nd, . . . , (n−1)-th switches. Then, the 0-th switch is a normally-open two-way switch and other switches are three-way switches. The first terminal of the 0-th switch is connected to the power source 236 and the second terminal thereof is connected to the common terminal of the 1st switch. For the k-th switch (k being an integer and 0<k<n−1), the common terminal thereof is connected to the normally-open terminal of the (k−1)-th switch, the normally-closed terminal thereof is connected to the k-th ignition circuit, and the normally-open terminal thereof is connected to the common terminal of the k-th switch. For the (n−1)-th switch, the common terminal thereof is connected to the normally-open terminal of the (n−2)-th switch, the normally-closed terminal thereof is connected to the (n−1)-th ignition circuit, and the normally-open terminal thereof is connected to the n-th ignition circuit.

In FIG. 22A the controller 234 is shown as comprising three switches 238A to 238C for controlling three well-stimulation apparatuses 120. The switch 238A is a normally-open two-way switch and switches 238B and 238C are three-way switches. The activation pressures for switches 238A to 238C are P1<P2<P3.

Switch 238A is connected to the power source 236 and the common terminal of switch 238B. The normally-closed terminals of switches 238B and 238C are connected to the ignition units 232A and 232B. The normally-open terminal of switch 238B is connected to the common terminal of switch 238C. The normally-open terminal of switch 238C is connected to the ignition unit 232C.

As shown in FIG. 22B, a fluid pressure P (P2>P>P1) is first applied to the switches 238A to 238C. Switch 238A is closed, and the ignition unit 232A is activated for well stimulation. Then, the pressure P is increased such that P3>P>P2. Switch 238B is closed, and the ignition unit 232B is activated for well stimulation. Next, the pressure P is further increased such that P>P3. Switch 238C is closed, and the ignition unit 232C is activated for well stimulation.

In some embodiments shown in FIG. 23, the controller 234 comprises a processor 252 for activating the ignition circuits 232A to 232C. A pressure sensor 254 such as a pressure transducer is coupled to the processor 252 for converting a fluid pressure P to an electrical signal for inputting to the processor 252. A power source 236 provides power to the processor 252 and the ignition circuits 232A to 232C. The controller 234 may use different pressure to activate different ignition circuits 232A to 232C with an order from downhole to uphole as described above.

In some embodiments of the present disclosure, the controller 234 is at the surface and is wired to the well-stimulation apparatuses 120 through the line 108. An operator may manually operate the controller 234 for well stimulation. Alternatively, the controller 234 may be programmed to automatically control the apparatus 120.

In some alternative embodiments as shown in FIG. 24 to FIG. 25C, a knuckle connector 262 may be used for flexibly coupling the apparatus 124 to the line 108.

FIG. 24 shows one non-limiting embodiment of the knuckle connector 262 as comprising a central portion 264 and two coupling portions 266 that are rotatably coupled to the two ends of the central portion 264 via respective universal joints (u-joints) 268. Each u-joint 268 is rotatable in 2-dimensions or alternatively 3-dimensions as needed.

One of the two coupling portions 266 is used for coupling the knuckle connector 262 to the line 108 and the other is used for coupling the knuckle connector 262 to a well-stimulation apparatus such as the well-stimulation apparatus 120 described above.

The knuckle connector 262 provides flexibility in positioning the well-stimulation apparatus 120 relative to the line 108 when one is misaligned from the other. As shown in FIG. 25A, the line 108 may travel in the wellbore 102 directly down the center thereof. In this case, the two coupling portions 266 of the knuckle connector 262 are aligned, and the knuckle connector 262 remains straight.

In some situations, as shown in FIG. 25B, the line 108 may travel straight, but off-center relative to the axis of the wellbore 102. In this case, the knuckle connector 262 is shown hinged to compensate for the axial misalignment between the well-stimulation apparatus 120 and the line 108.

In some situations, as shown in FIG. 25C, the line 108 may experience some bending or buckling. The knuckle connector 262 hinges to compensate for the axial and angular misalignments between the well-stimulation apparatus 120 and line 108.

In some embodiments of the present disclosure, the knuckle connector 262 is a separate component from the apparatus 120. In some alternative embodiments, the knuckle connector 262 may be an integrated portion of the apparatus 120. In these embodiments, the well-stimulation apparatus 120 is rotatably coupled to the central portion 264 via a first u-joint 268. The central portion 264 is rotatably coupled to a coupling portion 266 via a second u-joint 268. Therefore, the well-stimulation apparatus 120 may be coupled to line 108 or other subs via the coupling portion 266. In some embodiments of the present disclosure, the knuckle connector 262 may be an integrated portion of the line 108.

As will be appreciated by those skilled in the art the knuckle connector 262 is not limited to hinged connections and other types of flexible connections that can compensate between a misaligned position of the line 108 relative to the well-stimulation apparatus 120 are useful.

FIG. 26 shows an alternative embodiment of the sealing assembly 128A where the actuation body 154 is housed within a central bore of the sealing assembly 128A. Optionally the actuation body 154 is held within the central bore by a retainer nut 129 or other similar structure. In this embodiment fluid communication is provided between the actuation-propellant chamber 208 and the piston housing 202 by a gas channel 212A.

In some embodiments of the present disclosure, the sealing elements 122 are first actuated to form the isolated portion of the wellbore 102, and then the stimulation gas-generator assembly 126 is activated to generate the high-pressure gas for stimulating the isolated portion of the wellbore 102.

In some embodiments of the present disclosure, the actuation gas is not maintained after it actuates the sealing elements 122 to their active condition. In some alternative embodiments, the actuation gas behind the pistons 204 is maintained during the stimulation process to maintain the sealing elements 122 in the active condition, and then the pressure generated by the actuation gas is released for articulating the well-stimulation apparatus 120 into the dormant condition.

In some embodiments of the present disclosure, the sealing elements 122 are actuated by using the actuation gas generated by the actuation body 154. In some alternative embodiments, the sealing elements 122 may be actuated by other types of actuation mechanisms including, but not limited to: a hydraulic-pressure based mechanism, a pneumatic pressure based mechanism, a mechanical mechanism such as a spring, electric motor, electric solenoid, or a combination thereof.

In some embodiments of the present disclosure, the spring 192 is used for biasing the sealing elements 122 to the dormant condition. In some alternative embodiments, the sealing elements 122 may be biased to the dormant condition by multiple springs, or by other mechanisms such as a gas generator, a hydraulic-pressure based mechanism, a pneumatic-pressure based mechanism, a mechanical mechanism such as a spring, electric motor, electric solenoid, or a combination thereof.

In some embodiments of the present disclosure, the electrical ignition circuit 232, including the electrical actuation-activation devices 214 and the electrical stimulation-activation device 148, are used for well stimulation. In some further embodiments, other means such as pressure-activated firing heads, explosive primer cord, and the like, may be used for igniting the propellant for actuating the sealing elements 122 and the stimulant material 146 for stimulating production of hydrocarbons from the geological formation 106 into the wellbore 102.

In some embodiments of the present disclosure, the stimulation gas-generator assembly 126 may comprise two or more tie rods 132 that are positioned within one stimulant-material container 134. In some other embodiments of the present disclosure, the stimulation gas-generator assembly 126 may comprise a plurality of tie rods 132 and one or more stimulant containers 134.

In some embodiments of the present disclosure, the stimulation gas-generator assembly 126 may comprise a single type of stimulant material 149, or a mixture of two or more types of materials. Similarly, the actuation body 154 may comprise a single type of propellant or a mixture of two or more types of propellants. Moreover, the stimulation gas-generator assembly 126 and the actuation body 154 may use the same propellant material and the same propellant mixture or different propellants and/or different propellant mixtures.

In some embodiments of the present disclosure, the controller 234 comprises a power source 236. In some alternative embodiments, the controller 234 does not comprise any power source. Rather, a power source 236 external to the controller 234 is used.

Table 1 below lists some non-limiting examples of dimensions of the above described well-stimulation apparatus 120 in some embodiments of the present disclosure for use in a 13.51b-4.5 inches wellbore casing (with an inner dimension (ID) of 3.92 inches):

TABLE 1 Dimensions Overall length of the well-stimulation about 132 inches (11 feet) apparatus 120 Outer dimension (OD) of the sealing about 3.75 inches assembly 128, in the dormant condition OD of the sealing assembly 128, in the about 3.92 inches active condition Length of the sealing assembly 128 (approx.) about 16 inches Length of the tie rod 132 about 100 inches OD of the tie rod 132 about 2 inches ID of the stimulant-material container 134 about 2 inches OD of the stimulant-material container 134 about 3.75 inches Volume of the stimulant-material container about 790 cubic inches 134 (approx.)

Without being bound by any particular theory, the well-stimulation apparatus 120 described herein avoids the massive use of water for fracturing. Moreover, by using the well-stimulation apparatus 120, the rapid generation of high-pressure gas causes local disaggregation and shear dislocation along the fracture planes. Therefore, no proppant or sand is required.

Without being bound by any particular theory, the well-stimulation apparatus 120 described herein creates longer fractures through a longer deflagration time (for example between about 10 milliseconds to about 20 seconds), and is suitable for fracturing in horizontal wellbores. The well-stimulation apparatus 120 described herein substantially isolates a portion of the wellbore to focus the energy of the pressure event into the target portion of the geological formation. Moreover, a plurality of the apparatus 120 may be cascaded on a single line 108 for stimulating a plurality of wellbore zones in one run.

Table 2 below shows a comparison between the prior-art hydraulic fracking, the prior-art propellant-based fracturing, and the well-stimulation apparatus 120.

TABLE 2 Comparison of stimulation processes Prior-art Prior-art propellant- The well- hydraulic based stimulation fracturing fracturing apparatus 120 Pressure About 1 to 20 hours About 300 to About 10 milli- Event 500 milli- seconds to about Duration seconds 20 seconds Peak Pressure Minimum pressure 20,000 psi about 10,000 to (about 5,000 psi) to about 50,000 psi overcome over- burden on the formation Fractures Only lowest High and low High and low Opened cohesion cohesion cohesion frac- fractures fractures tures and new fractures Fracture 2 radially opposed 4 to 8 radial 4 to 8 radial Pattern fractures fractures fractures Fracture Long Short Long Length Well Types Vertical and Vertical wells Vertical and horizontal wells horizontal wells Applications New wells, re- Re-entries/ New wells, re- entries (with re-stimulation entries and specialized damaged comple- casing) tions Water Average 5 million Drilling fluid Drilling fluid Requirement gallons per well Proppant 300,000 to Self-propping Self-propping Requirement 4,000,000 by local by local pounds of sand disaggregation disaggregation 

1. A well-stimulation apparatus comprising: a tie rod with a first end and a second end; a stimulant-material container that is configured to be secured about the tie rod; and a sealing assembly that is couplable to the first end of the tie rod, the sealing assembly being actuatable between a dormant condition and an active condition for isolating a portion of a wellbore.
 2. The well-stimulation apparatus of claim 1, further comprising a second sealing assembly that is couplable to the second end of the tie rod.
 3. The well-stimulation apparatus of claim 1, further comprising a fastener for coupling the first sealing assembly and the second sealing assembly to the first end and the second ends respectively of the tie rod.
 4. The well-stimulation apparatus of either claim 1, wherein the stimulant-material container comprises one or more sleeves that are configured to receive stimulant material therein.
 5. The well-stimulation apparatus of claim 4 wherein the stimulant material is deflagratable for generating a pressure event.
 6. The well-stimulation apparatus of claim 5, wherein the tie rod is configured to bear a tensile load that is generated by the pressure event.
 7. The well-stimulation apparatus of claim 5, wherein when the sealing assemblies are in the active condition, the pressure event is directed in a radial outward direction from the well-stimulation apparatus.
 8. The well-stimulation apparatus of claim 5, wherein the pressure event has a peak pressure of between about 10, 000 pounds per square inch (psi) and 50, 000 psi.
 9. The well-stimulation apparatus of claim 1, further comprising at least one stimulation-activation device for igniting the stimulant material.
 10. The well-stimulation apparatus claim 1, wherein each of the first sealing assembly and the second sealing assembly comprises: a mandrel; a plurality of sealing elements positioned about the mandrel, each of the plurality of sealing elements comprises an outer edge that is configured to engage an inner wall of a wellbore or a tubular therein; and an actuation body for actuating the plurality of sealing elements to move from the dormant condition to the active condition.
 11. The well-stimulation apparatus of claim 10, wherein the actuation body is at least one of: an actuation gas-generator, a hydraulic-pressure driven mechanism, a pneumatic-pressure driven mechanism, a mechanical mechanism such as a spring, an electric motor, an electric solenoid, and combinations thereof.
 12. The well-stimulation apparatus of claim 10, wherein the plurality of sealing elements are stacked about the mandrel at an acute angle with respect to a longitudinal direction of the well-stimulation apparatus.
 13. The well-stimulation apparatus of claim 10, wherein the plurality of sealing elements are swingable between an angle of repose α in the dormant condition and an angle of attack β>α in the active condition.
 14. The well-stimulation apparatus of claim 13 wherein the angle of repose α is between about 0° and about 75°.
 15. The well-stimulation apparatus of claim 13, wherein the angle of attack β is between about 10° and about 80°.
 16. The well-stimulation apparatus of any claim 1, further comprising a knuckle that is couplable to one end of the well-stimulation apparatus, and the knuckle comprises: a central portion rotatably coupled to well-stimulation apparatus via a first joint; and a coupling portion rotatably coupled to the central portion via a second joint.
 17. A sealing assembly for isolating a portion of a wellbore, the sealing assembly comprising: a plurality of sealing elements that are actuatable between a dormant condition and an active condition; and an actuation gas-generator for generating a gas flow for actuating the plurality of sealing elements from the dormant condition to the active condition.
 18. A knuckle connector for coupling a first downhole apparatus to a second downhole apparatus, the knuckle connector comprising: a central portion rotatably coupled to a first joint and a second joint; a first coupling portion rotatably coupled to the central portion via the first joint; and a second coupling portion rotatably coupled to the central portion via the second joint.
 19. A knuckle connector for coupling a first downhole apparatus to a line from surface, the knuckle connector comprising: a central portion rotatably coupled to having a first joint and a second joint; a first coupling portion rotatably coupled to the central portion via the first joint; and a second coupling portion rotatably coupled to the central portion via the second joint.
 20. A well-stimulation system comprising: a plurality of n well-stimulation apparatuses for isolating a plurality of n downhole portions of a wellbore and stimulating the plurality of isolated wellbore portions, n being an integer greater than or equal to 1, and each well-stimulation apparatus comprising an activation circuit for activating at least a well stimulation process thereof; and a controller for controlling the activation circuits of the plurality of well-stimulation apparatuses, the activation circuits being numbered from downhole to uphole as the first, second, . . . , the n-th activation circuit; wherein the controller comprises n pressure-actuated switches, with the 0-th switch being a normally-open two-way switch and the first to the (n−1)-th switches being three-way switches, wherein the first terminal of the 0-th switch is connected to a power source and the second terminal thereof is connected to the common terminal of the 1st switch, wherein for the k-th switch (k being an integer and 0<k<n−1), the common terminal thereof is connected to the normally-open terminal of the (k−1)-th switch, the normally-closed terminal thereof is connected to the k-th activation circuit, and the normally-open terminal thereof is connected to the common terminal of the k-th switch, and wherein for the (n−1)-th switch, the common terminal thereof is connected to the normally-open terminal of the (n−2)-th switch, the normally-closed terminal thereof is connected to the (n−1)-th activation circuit, and the normally-open terminal thereof is connected to the n-th activation circuit.
 21. The well-stimulation system of claim 20 wherein the m-th switch is switchable under a threshold switching pressure P_m, with m being an integer and 0≤m≤n−1; and wherein P_0<P_1< . . . <P_(n−1).
 22. A method for stimulating a targeted portion of a geological formation, the method comprising steps of: isolating a portion of a wellbore that is proximal the target portion by actuating one or more sealing elements into an active condition; deflagrating a stimulant material for generating a pressure event; and focusing at least part of an energy of the pressure event into the targeted portion. 